High inspired concentration of oxygen are often a necessary and lifesaving therapy for the treatment of many adult and pediatric patients. Unfortunately exposure to high partial pressures of oxygen are toxic with the lung being the organ that is most sensitive. The toxic effects of oxygen plays a critical role in the pathogenesis of several clinically important lung diseases including bronchopulmonary dysplasia, adult respiratory distress syndrome, and tracheobronchitis. Extensive research efforts in animals have classified specific oxygen-dependent responses, namely the oxygen sensitive nature of pulmonary microvascular endothelial cells and the relatively oxygen resistant capacity of pulmonary type II alveolar epithelial cells. Similarly, other studies have demonstrated different developmental responses to hyperoxia in fetal, neonatal, and adult animals. These differences may be a result of the relatively low oxygen environment for the fetus and the need to prepare for a rather rapid transition to an increased oxygen environment at birth. The overall goals of this research is to increase our understanding of oxygen toxicity by characterizing at the molecular level the cell's response to high ambient oxygen tensions. The first goal of this project is to identify hyperoxia-responsive genes in the rat pulmonary microvascular endothelial cells and pulmonary type II alveolar epithelial cells. We are interested in genes that show a primary response to oxygen tension. Whether it be an induction of the gene with an increase in MRNA levels or a repression with a decrease in MRNA. To determine the time frame of the response, we will utilize two- dimensional protein gel electrophoresis as a direct molecular assay. Based on these studies a subtracted CDNA library will be constructed and hyperoxia-responsive CDNAS isolated by differential screening using subtracted anchored polymerase chain reaction probes. One isolated CDNA from each cell type will be characterized by sequence analysis and verified as representing a hyperoxia-responsive gene by Northern analysis. The isolated CDNAS will be furthered characterized by Northern analysis as to its cell specificity and its developmental characteristics. To determine the regulatory patterns of the hyperoxia- responsive genes, specific inhibitor studies and nuclear run-on assays will be performed.